Inflatable restraint systems or “airbag” systems have become a standard feature in most new vehicles. These systems have made significant contributions to automobile safety; however, as with the addition of any standard feature, they increase the cost, manufacturing complexity and weight of most vehicles. Technological advances addressing these concerns are therefore welcomed by the industry. In particular, the gas generator or inflator used in many occupant restraint systems tends to be the heaviest, most complex component. Thus, simplifying the design and manufacturing of airbag inflators, while retaining optimal function, has long been a goal of automotive engineers.
Typical inflators are constructed having an elongate metallic body. Because many inflators utilize pyrotechnic gas generant compounds to produce inflation gas for the associated airbag, the inflator structure is necessarily robust, making such inflators correspondingly heavy. The long term success of driver-side and passenger side inflatable restraint systems has prompted automotive manufacturers to increasingly investigate and implement side impact inflatable restraints, as well as inflatable airbelts. Because the inflatable systems are typically mounted in the vehicle roof pillars, doors or seats, mounting space can be at a premium. Moreover, coupled with inherent difficulties in engineering inflators capable of producing the relatively small, punctuated inflation charges typical of side impact airbags and airbelts, such systems present a unique set of challenges to designers. Engineers have developed numerous designs for optimizing weight, operation and assembly; however, the pressure to downsize components and reduce manufacturing challenges continues to be acute.
Accompanying the need for ever simpler and more elegant designs is the desirability of inflators that are relatively robust yet capable of reliable operation even after storage periods of several years. One problem in particular associated with long periods between installation in a vehicle and activation of the inflator relates to mechanical degradation of the gas generant or propellant material. Many gas generants are provided in a solid, typically tablet form. Jostling of the propellant within the inflator can have the undesirable effect of breaking or crumbling the propellant tablets, reducing their efficacy in some cases. Various spring-biased mechanisms for constraining movement of the propellant tablets have been proposed; however, these systems tend to increase manufacturing complexity and cost, and add extra components to the inflator, adding to the weight of the system.